Method of preventing overheating of rubber in screw-type extruding machines



. DAY

VER HEA'II UDI 6 1,800,180 m OF RUBBER gmcaxuss Apnl 7, 1931. R 5

METHOD OF PREVENTING O IN SCREW TYPE EXTR Filed Nov grwe mtow RoAph B. Dan

Patented Apr. 7, 1931 UNITED. ,S-VTATES'PATENT. OF

mun B. may, or nxnoif, 0x10, xssmxoa 'IOf m eoonvm ruin a 1mm column, or anon, 0310, a coaroamox or one 1 Application filed liovember a, ma. swarm. 405,149.

This invention relates to a method of oper ating rubber manipulating machinery and. it has particular relation to the operation of extruding machines of the type in which a screw is employed to force unvulcanized rubber through a die.

. One object of the invention is to provide a method of operating machines of the abovedesi ated character. whereby the rate of production is materiall increased. 1

Another object 0 the invention is to prevent scorching of rubber compounds which are being extruded through the machine.

An additional object of the invention is to reduce the consumption of power required to operate the machine. I

In extrudin unvulcanized rubber b means of a mac ine of the screw'type, muc power is consumed in overcoming friction between the surfaces of the machine and the rubber, and also in overcoming the friction,

In order to reduce the temperature of the machine and the stock, it is customary to provide a jacket about the cylinder of the machine and to form a longitudinally ex-. tending passage through the core of the screw. A'cooling medium, such as water, is,

circulated through the space between the jacket and the cylinder and also through the passage in the screw. In this way, a portion of the excess heat is carriedaway by convection. In the practice of such processes, water having a temperature approximating that of the atmosphere (approximately 7 4 F.) is usually employed as a cooling fluid. However, rubber is a very poor conductor of heat and as a result the heat;

generated within the interior of the rubber mass, due to the kneading action created by the relative movement between the walls of the cylinder and the surface of the screw,

does not escape to the cooled surface with s'uflicient rapidity. Therefore, it is necessary to maintain the rate of o ration of the machine at a relatively low v ue in order to prevent excessive temperatures within the in.- terior of the rubber even when the coldest practicable cooling fluid is employed in the machine.

This invention involves the discoverythat by employing a relatively hot fluid within thescrew and throat of the extruding machine, friction .between the surface of the screw and the rubber compound is greatly reduced at the same time back pressure upon the stock, created by friction within the throat of the machine, is also maintained at a m1n1mum value, and as a result, the compound is advanced more rapidly through the machine, and the kneadin action upon the compound betweenthe sur aces of the screw and the cylinderis reduced. Therefore, contrary to what would naturall be expected, increase in the temperature 0 the screw results in a reduction of the temperature of the stock passing throu h the die of the machine.

For a better un erstanding of the invention, reference may now be had to the accompanymg drawings, forming a part of the specification, of which the single figure is a fragmentary cross-sectional view of an extru mg machine showing the cylinder walls and the screw contained therein.

In practicing the invention, an extruding machine of conventional ty e is em loyed. This machine comprises a cyiinder 10 having inner and outer walls 11 and 12, respectively,

defining a chamber 13 for facilitating the circulation of a cooling fluid. Rubber compound is introduced into the cylinder adjacent one end thereof through an opening or hopper 14. The forward end of the cylinder 10 is provided with athroat portion 16 having an annular chamber 17 formed therein for receiving a heating fluid. The throat portion, in turn, is provided upon its forward side with a plate 18 which has a slightly I]: scimw-mr: nxrnnnnre,

tapered circular opening 19 therein, which is disposed in coaxial alignment with the throat portion 16 andthe cylinder 10.

The disc or plate 18 constitutes .a support for a die or head portion 21 having afrustoe conical bore which .is normally. disposed in coaxial alignment with the throat portion 16 and the cylinder 10, The member21, like the portion 16, is provided with an annular chamber 22, which is connected toa suitable source of supply of' heating fluid- (not shown).

In order to advance the rubbencompound-j through the cylinder, a rotatably driven.

screw 23 of conventional. designis disposed 1 within the cylinder. The core-of the screw-is formed with a longitudinall extending passageway 24 to provide for t e circulation of,

a heating fluid. Theforward end of the screw is provided with atapered bearing 26, l

in which is disposedtherearend of a spindle or mandrel 27 which'isnormally disposed coaxially within the members 16,. 18' and 21;;

The mandrel is maintained inposition within those members by'means of' aspider 28 having an outer rim' 29,-w-hich isdisposedwithin grooves 31 and-32 formedwithin the inner peripheries of the members 16 and 18,- The spider. also has radially extending spokes 33 which interconnect the spindle 27.

and the rim 29. If. desired, the spindle-27" may be formed with a longitudinalchamber 34 which communicates through passageways (not shown) in the spokes 33 wltha suitable source ofheating fluid. Thefor-v ward end of the mandrel 27 fits within fa..depression within the rear portion of an 1nternal die element 36, which is disposedw-ithin the head or die 21,- andwhich is securedi,

thereto by means of abolt .37jand a nut:38;,

In the operationof the machine, rubber compound which is introduced through; the

opening or hov per 14, is-driven vforwardlyby. the screw an the spokes 33 of the spider; 31, finally being forced from the machine -through" the annular space between the die members 21 and 36.. During the operation of the machine a con stant flow of cooling fluid, whichis usually at a temperature approximating that of the atmosphere (approximately 74 or 75 F.)

' sults in the local heating ofthe stock which is maintained withinthe space 13. At the same time, a flow of fluidhaving a relativelyhigh temperature is maintained within the. passageway 24 of the screw. 23 The temperature of this fluid may vary within relatively.

same value as that of the fluid within the pas sageway 24 of the extrudingscrew.

The employment of a fluid'ofrelatively high temperature in the screw apparently re,-

comes into contact with the latter member and, as a result,'a film of rubber adjacentthe' is forced T: outwardly, between] surface of';the screw s-isso-soft'ened asto cause it toact as a lubricant .betweenthermainbody of stock andi the surface of th'e screwa Be cause of:therelatively-lowzcoeflioientiof heat conductivity of the rubber, the heat fromthe screw does-not have time-to penetrate the mass-of 5 rubber 1 to 'an.y,: appreciable degree. This lubrication, .of. thecontacting surfaces greatly reduces the-,- friction between the ,screw. andith'e stock and'thus prevents-excessive screw; surface friction and-kneading of. the stock: as it passes.-,-tl1rough; thecylinder.- Therefore, the;excessive.increase ofzitemperature within the, stockdue to internal frictionoccasioned.- by the kneading isi greatlyreducedii. Similar lubricatingtefiectsand a resultant reduction. of" resistance is. also.-.obtained by; the circulation Of. heated fluid in the passages .orchamb'ers 17-,222aand1 341 The increase efficiency attending-the use of heated? fluid;- in the screw. and throat: of an extrudingmachine-is clearly. indicated .by the attached data in which; the-results. obtained by operatingyaizmach ine according. to standard practice .are cQmparedQWith the results obtained byoperat'ingthe same machine in aceordancewith the principles :ofthis invention; In the,first-casefWater at. a tempera- .ture of; approximately-7 5 Eiwasemployedin b0th screw-throatand:harrel. Inthe second case water at- F.- was: employed in the barrel .while that in :the screw and throat was, increased approximately to 170 F. The speed of=the screw andthroatiwas so regulated in bothcases thatthetemperaturesaof the stock at output wereidentical;

Output R. P. M 1

- (feet per W minute);

Standard practicum.-- 101 b 43.5 Hot water in screw-.. 140v 71. 5

It is thus apparent thattheincrease in the temperature ;of the waterin the above indicated'parts. of, the machine permits a'great lncreasein the output of'the machine without any increase in the temperature of'the stock-atoutput.

Although I have illustrated only one form,

which the -invention may assume, .andhave described in detail only a single application thereof, it will beapparent-to those skilled inthe art that the invention is-notso limited, butthat various modifications may be made therein without departing; from the spirit ofthe invention or, from thescope of theappended claims.

What I claim is:

1.1 A, method of'extruding rubber. from a machine cornprising a cylinderand a core disposed withmthe cylinder, one of which ele-.

ments is provided with a screw-thread which comprises; cooling the... unthreaded member" while heat'mg' the threaded member;

2. A method of extrudin rubber which comprises passing it throug a screw tjyl'pe extruding machine in which the outer cy 'nder is subjected to the action of a cooling fluid while the screw is subjected to the action of a fluid of materially higher temperature than the temperature of the cooling fluid.

3. A method of extruding rubber which comprises passing it through a machine comprising an outer cylinder and an inner core disposed longitudinally within the cylinder and rotatable therein which comprises cooling the cylinder with a fluid at approximately room temperature and heating the screw with fluid at a temperature ranging from 120 to 190 F.

4. A method of extruding rubber. from screw typeextruding machines which comprises passing the rubber through the machine while maintaining the temperature of the screw and the throat of the machine at a substantially higher temperature than the barrel of the latter.

5. A method of operating an extruding machine for extrudin rubber havin a cylinder, a throat for t e cylinder and a screw within the cylinder for forcing the rubber therethrough which comprises circulating a relatively cool fluid about the cylinder and a fluid at a temperature of 120 to 190 F.

through the screw and the throat of the machine.

6. A method of operating a machine for extruding rubber which comprises positively cooling certain parts of the machine to temperatures below that of the rubber compound being extruded while other parts of the machine are heated to temperatures materially'above that of the rubber compound 40 whereby to increase the frictional resistance between the compound and the cooled parts of the machine, and to decrease the resistance between the compound and the heated parts.

4 In witness whereofllhave hereunto signed I my name.

Si ed at Akron, in the county of Summit and tate of Ohio, U. S. A., this 4th day of November, 1929.

RALPH B. DAY; 

